Preparation of 2,5-dibromoterephthalic acid

ABSTRACT

2,5-dibromoterephthalic acid, an intermediate used for flame retardant applications, is prepared from terephthalic acid, in a single step, by brominating terephthalic acid in chlorosulfonic acid or fluorosulfonic acid, containing sulfur trioxide and employing an iodine catalyst. The reaction is carried out under mild conditions. The products, 2,5-dibrometerephthalic acid, with lesser amounts of terephthalic acid, bromoterephthalic acid, tribromoterephthalic acid, and tetrabromoterephthalic acid, are recoverable either by filtration of the cooled bromination suspension or by distillation of the chlorosulfonic or fluorosulfonic acid solvent and the further hydrolysis of the brominated terephthalic acid product.

United States Patent [191 Knobloch 1 July 8,1975

[ PREPARATION OF 2,5-DlBROMOTEREPHTHALlC ACID [75] Inventor: James O. Knobloch, Naperville ill.

[73] Assignee: Standard Oil Company, Chicago, Ill.

[22] Filed: Dec. 29, 1972 [2H Appl. No.: 319,500

[52] US. Cl...... 260/515 A; 260/544 D; 260/544 M [5 1] Int. Cl. C076 63/26; C070 63/30 [58] Field of Search 260/515 A, 544 D. 544 M [56] References Cited UNITED STATES PATENTS 4/1935 Mueller 260/515 7/l964 Wilkinson 260/5l5 Primary Examim-r.lames A. Patten Attorney. Agent, or Firm-William H. Magidson; Arthur G Gilkes; William T. McClain [57] ABSTRACT 2,5-dibromoterephthalic acid, an intermediate used for flame retardant applications. is prepared from terephthalie acid, in a single step. by brominating terephthalie acid in chlorosulfonic acid or fluorosulfonic acid, containing sulfur trioxide and employing an iodine catalyst. The reaction is carried out under mild conditions. The products, 2.5-dibrometerephthalic acid, with lesser amounts of terephthalic acid. bromoterephthalic acid. tribromoterephthalic acid, and tctrabromoterephthalic acid, are recoverable either by filtration of the cooled bromination suspension or by distillation of the chlorosulfonic or fluorosulfonic acid solvent and the further hydrolysis of the brominated terephthalic acid product.

4 Claims, N0 Drawings 1 2 PREPARATION OF 2 5-[)[BROMOTEREPHTHALIC containing sulfur trioxide. Bromine and an iodine cata- ACID lyst are added. The reaction proceeds and is held at a y temperature of between 40 to 80C. preferrably. 40 BACKGROUND OF THE INVENTION to 55C. for a period of from l to lil hours. When Th recent gmwth i h use f fl bl r i l fluorosulfonic acid is used as the solvent there is very has increased the incidences of damage and personal little ifany substitution of fluorine in the aromatic ring i j y b fire, Con ern for bli f t h t d of terephthalic acid. since fluorosullonic acid is a more government agencies to impose stricter fl bili stable compound. therefore fluorosulfonic acid is a standards for those applications where synthetic matehighly deslmhlc SOIWN- rials are used. Asa result. the use of halogen containing The rfiuclion Occurring can hc Yeprcscmcd y thc compounds. particularly chlorine and bromine containt cqumimi ing compounds as additives or as an integral part of a The preparation of 2.5-dibromotcrephthalic acid of finished polymer to impart fire retardant properties to the present invention is more specifically illustrated by polymeric materials is a rapidly growing industry of the following examples:

great commercial importance. Such compositions can be utilized in those areas of application where fire is EXAMPLE I likely to occur and to prevent substantial danger or hazard to individuals or property. Examples of such appli cations are use of polymeric material in household uppliances, building materials. the auto industry. the air craft industry. and others. The seriousness of the potential danger from combustible materials has spurred activity on the part of various government regulatory bodies. Thus. several government agencies are setting flammability standards for autos. aircraft, carpets and other articles made from synthetic polymeric materials. In response to these pressures. makers of synthetic polymeric materials are increasing their efforts to impart flame retardant properties to their products. 4(

An object of this invention is to provide an intermediate compound containing bromine that may be used to form fire retardant polymeric products. Such products would include synthetic polyesters that may find use in a variety of applications where a high degree of flame 45 retardancy or self-extinguishing properties are desir- The bromination apparatus consisted of a 250 ml. 3- neck flask equipped with a heating mantle. a theremometer in the liquid phase. an l'i-tray Oldershaw column equipped with a cold-finger (75C) reflux condenser. a liquid-dividing reflux head and a receiver cooled to 65C. Chlorosulfonic acid 98.5 grams) was added to the flask first; then with stirring l(l5.5 grams of sulfur trioxide was added (temperature rose to 46C) followed by 34.] grams terephthalic acid (TA). (The tcrephthalic acid used contained 0.94% isophthalic acid). The exterior of the flask was cooled so that the final temperature was 52C. The following day 0.5 grams iodine and 35.5 grams of bromine were added. Light was excluded by an aluminum foil flask cover. The flask was heated from 34 to C (pot temperature) in 26 minutes. then peaked at 55-6() /2C and settled back down to 4U44C after 7 minutes. The heating mantle was lowered during this exothermic part of the reaction and an ice bath was used. Thereafter heat able or,neceslsary' was applied. The reaction was held in the 4454C My mvemlon f the prepilmtmn f range for 7 hours. The column head dropped to 8 V2C dibromoterephthalic acid. a valuable intermediate to to o and tha reflux rat-m (Column return to tukc be used to form flame retardant polymers wherein off) was varied between 40:1 and 80:] to control the mine is reacted with terephthalic acid in chlorosulfonic pot temperature. Three milliliters of Sulfur dioxide or fluorosulfonic acid in the presence of an iodine catawere collected in the receiver lyst- The following day the 266.4 grams remaining in the An East German P -E 141750 lssuefj flask was centrifuged. and recycled three times to re- 1958- (3155311082) descnbes tetrabmm" cover most of solidsv The cake was then washed on the nation of phthalic anhydride in chlorosulfonic acid with Centrifuge with 50 m| 6618": Sulfuric acid The acid we a sulfur catalyst at temperature conditions of l45 to cake (85.3 grams) was Cautious. added m 3 0 m] ice y novel Process is distinguished from this water, digested 3 hours. cooled in an ice bath. and filmelhod in that it Unexpectedly allows tel'ephthallc acid tered. washing with 50 ml distilled water. After drying to be brominated to form 2.5-dibromoterephthalic acid 22 hours (at 50C d under a mummy h k under mild temperature conditions of from 40 to 80C, weighed 45 grams with lower temperatures desirable to minimize over- Th chlorogulfgnic id filt t (1113 grams) w bromination. allowed to stand near the steam bath to gradually absorb water. The following day it was poured on 400 SUMMARY OF INVENTION grams of ice, digested on the steam bath, cooled. fil- Pursuant to my invention, 2,5-dibromoterephthalic tered i h 25 l f di ill d water h) d h acid is best prepared by adding terephthalic acid to a d i d to yield 9.2 grams of solid material (called solution of chlorosulfonic acid or fluorosulfonic acid M th Li S lid The sulfuric acid wash (101.0 grams) was worked up in the same way as the chlorosulfonic filtrate to yield 7.8 grams of dry H 50 wash solids".

Each of the three solid samples were methylated with diazomethane alone and with tetrabromoterephtbalic acid as an internal standard. The methylated solutions were stripped of all excess diazomethane and ether under a vacuum at low temperature. Residues were analyzed by gas chromatography. Peak identifications were made by a gas-chromatograph attached to a mass spectrometer. The results are shown in Table 1 in area percent. Factors were known for the brominated terephthalic acids. so these are also reported (values in parentheses) as weight percent.

TABLE 1 dioxide gas. After cooling the solution weighed 934.8 grams and was divided into three weight aliquots.

The first aliquot (298.8 grams) was vacuum stripped maining were dried amounting to 37.3 grams. The inm frared spectrum as a KBr disc showed a strong carbonyl absorption at about 1.700 cm with very slight shoulders at 1.690 and 1.715 cm. 2.5-Dibromoterephtha1ic acid has a carbonyl abosrption at 1.700 cm. The carbon tetrachloride extract (filtrate) was stripped of sol- PRODUCTS FROM BROMlNATlON OF ThREPHTHALIC ACID: ANALYSES Table 11 shows the mole /E yields that were obtained.

vent under vacuum and reduced to 25.5 grams residue.

TABLE 11 Yield (Mole 7% on TA Charged) Centrifuge Mother H50.

C ake Liquor Wash Total Solids Tcrephthulic Acid (TA) .018 .032 050 BrTA .376 .110 486 Br- TA 61.8 .697 7.21 69.7 B TA .084 .1126 .044 .154 Br TA .434 3.87 1.04 5.33 Total 75.72

Thus a yield of 69.7 mole 7c 2.5-dibromoterephthalic From l 1.5 grams of this residue. we obtained 2.8 grams acid. showing an 89.1 wt7r purity was demonstrated. of sublimate and 3.6 grams of bottoms. The sublimate One major contaminent was observed in the crude has a carbonyl absorption at 1.772 cm which may be cake. that being bromochloroterephthalic acid. 55 due to 2.S-dibromoterephthaloyl bromide. since 2,5-

LE dibromoterephthaloyl chloride has a carbonyl absorp- EXAMP tion at 1.756 cm. This shift in carbonyl absorption is A l-liter 4-neck creased flask equipped as in Examalmost identical to the 1795 to 1810 difference beple 1 but without a column (a water-cooled reflux con- 60 tween acyl chloride and acyl bromide respectively redenscr was used in place ofcolumn) was used. The chaported by Dyer in Applications of Absorption Specrge consisted of 83.2 grams of freshly distilled terephtroscopy of Organic Compounds," Prentice-Hall 1965. thaloyl chloride (0.410 moles), 71 1.1 grams chlorosulp 35. fonic acid. 83.4 grams sulfur trioxide 1.043 moles). A second aliquot 3614 grams) ofthe chlorosulfonic 1.01 grams iodine and 70.0 grams of bromine (0.438 .5 acid solution was vacuum stripped (78C pot maximoles). The reaction solution was heated from 32 to 65C in 1 hour. then held at 65-74C for 3% hours. A little bromine was lost. carried off with escaping sulfur mum) to a residue of 137.8 grams. This was allowed to contact moist air overnight and then mixed with 200 ml water and digested on the steam cone four hours. It was then cooled in an ice bath. filtered. and washed with ml distilled water. The 58.9 grams of dry residue was refluxed 24 hours in 735 ml absolute methanol. On cooling. a 2L6 grams (dry wt.) insoluble cake was recovered. The methanol solution was evaporated to leave 39.0 grams dry residue. Samples of both products were further esterified with diazomethane and analyzed employing an internal standard. The results are shown in Table III.

TABLE lll PRODUCTS FROM BROMlNA'llON OF TEREPHTHALOYL CHLORIDE: HYDROLYZEI').

REACTED WITH (H OH AND (H N Area I: (wt '/r 6 The components for which factors were known for converting area to weight percent give the following yields:

Yield (mole "2 on lA Charged) When l'luorosulfonic acid was used in place of chlorosulfonic acid. the results were very similar to the examples shown. except that there was almost no fluorine substitution in the aromatic ring of terephthalic acid.

What I claim is:

l. A process for the preparation of a 2.5- dihromotcrephthalic acid compound. which comprises reacting a tcrephthalic acid compound in a solution of chlorosull'onic acid or fluorosulfonic acid containing sulfur trioxidc. in the presence of iodine with bromine at 40 to C.

2. The process of claim I. wherein said temperature is 40 to 55C.

3. The process of claim 1. wherein said terephthalic acid compound comprises terephthalic acid.

4. The process of claim I. wherein said terephthalic acid compound comprises tcrcphthaloyl chloride. 

1. A PROCESS FOR THE PREPARATION OF A 2,5-DIBROMOTEREPHTHALIC ACID COMPOUND, WHICH COMPRISES REACTING A TEREPHTHALIC ACID COMPOUND IN A SOLUTION OF CHLOROSULFONIC ACID OR FLUOROSULFONIC ACID CONTAINING SULFUR TRIOXIDE, IN THE PRESENCE OF IODINE WITH BROMINE AT 40O TO 80*C.
 2. The process of claim 1, wherein said temperature is 40* to 55*C.
 3. The process of claim 1, wherein said terephthalic acid compound comprises terephthalic acid.
 4. The process of claim 1, wherein said terephthalic acid compound comprises terephthaloyl chloride. 